The latest version of the mobile OS launched weeks ago, but the issue is finding increasing traction as both Nokia 920 and HTC 8X owners take to forums to complain.

"I got my HTC 8X on 3 November, and didn't notice any reboots the first few days," said adesonic on the Microsoft forum, as first reported by The Verge.

"Since then, reboots have been becoming more frequent – five today so far. I seem to remember a similar problem with the original WP7 on my HD7, it was fixed by an update. This needs fixing quickly - the device cannot be relied upon in its current state."

Reboots so far during many different situations. I've heard from someone who had no problems on his 920 until he inserted the Micro SIM

Microsoft has yet to publicly acknowledge the issue, despite being informed by users and having several pages of complaints on its own forums.

The affected users have been unable to pin down the problem to any particular app, handset or function, which has led many to believe the problem is related to the OS itself.

"It's not user or app dependent as far I can say," posted one user. "Reboots so far during many different situations. I've heard from someone who had no problems on his 920 until he inserted the Micro SIM."

Over on the Windows Phone Central forum, there's also growing frustration at the lack of a response from Microsoft, although it's understood tech support teams are looking into the issue.

"I've been tweeting with Winphone support for the last 24 hours, informing them about the rebooting issue - I also informed them that hundreds of people are reporting this rebooting issue," said Strokee.

"Microsoft said that it is now looking into the matter and will respond to me via Twitter."

Says that its something to do with "overfilling" the storage. I have 32G in my 7pro and random reboots occur if its filled beyond 16G.As its an unofficial upgrade, I wager that this issue has never been properly tested on WP7x at least.

I have this problem also but in addition my Lumia 820 turns itself on in the middle of the night as well, sometimes leaving me with a flat battery, I have another issue in that my Mercs phone system won't transfer my contacts across this must be an issue with the latest Bluetooth spec but no one can give me awnser on that one so I have the old Lumia 800 in the car and that's works fine.